This invention relates to the use of dental compositions which exhibit an advancing contact angle of at least about 130.degree. relative to saliva, and in particular, to the use of dental filling composite materials comprised of a finely divided, inert inorganic filler and a hydrophobic binder system. The distinctive features attributable to the use of such dental compositions include the formation of restorations which, in relation to water, exhibit a low wettability, a high contact angle, a low absorption of water at equilibrium, a relatively high diffusion coefficient for water and ionic species, and a free surface energy change, .DELTA.F, which is positive.
An equation which describes the driving force for penetration of a liquid into a capillary space has been developed by O'Brien et al (J. Colloid & Interface Science, 26: 500 508, 1968). The equation relates the free surface energy change, .DELTA.F, to the surface tension of the liquid, .gamma..sub.1v and the contact angles of the liquid against tooth structure, .theta..sub.1, and the restorative material, .theta..sub.2. The equation is as follows: EQU -.DELTA.F=.gamma..sub.1v (Cos .theta..sub.1 +Cos .theta..sub.2)
If .DELTA.F is negative, then penetration of the liquid is spontaneous; whereas, if .DELTA.F is positive, outside pressure must be applied to force liquid into the capillary space.
The use of acrylic resins as binders in dental filling composites is disclosed for example, in detail in U.S. Pat. No. 3,066,112 to Bowen; U.S. Pat. No. 3,179,623 to Bowen; U.S. Pat. No. 3,539,533 to Lee, II et al; U.S. Pat. No. 3,540,126 to Chaug et al; U.S. Pat. No. 3,751,399 to Lee, Jr., et al; and U.S. Pat. No. 3,825,518 to Foster et al.
While such prior art acrylate resin compositions have been proven useful, it is known that many such compositions exhibit only limited resistance to wettability by water, and thus permit penetration or microleakage of saliva and other aqueous fluids at the margins of a restoration. Some of the compositions, for example, the fluoroalkoxyalkyl-2-cyanoacrylates disclosed in the above patent to Chaug et al are somewhat hydrolyzable and, therefore, biodegradable. Accordingly, while such materials are described as being useful as sealants, adhesives and coatings in the art of dentistry and medicine, these materials tend to be even more readily degradable in the mouth than the alkyl types of acrylate resins. Thus, even though the Chaug et al compositions might exhibit significant adhesion and bond strength to tooth structure, the bond strength will degrade with time, thus allowing penetration or microleakage of saliva and other aqueous fluids at the boundaries between the tooth and the fluoroalkoxyalkyl-2-cyanoacrylate composition.
The advancing contact angle of water on a fluorinated cyanoacrylate of the type described in the patent by Chaug et al is considerably lower than 130.degree.. For example, the advancing contact angle of water on Flucrylate cyanoacrylate, a fluorinated cyanoacrylate of the Chaug et al type obtainable from the Surgical Products Division of the Minnesota Mining and Manufacturing Co., is 97.degree..+-.3.degree..
The degradation of the bond strength of cyanoacrylates to bone has been demonstrated by Brauer et al (J. Biomed. Mat. Res. 13:593-606, 1979). Thus, the bond strength of isobutyl 2-cyanoacrylate decreased from 6.6 MPa to 2.0 MPa after six months storage in water, and the bond strength with the ethyl derivative decreased from 6.6 MPa to 0.2 MPa in one month. The bond strength at one day for fluorinated 2-cyanoacrylate was 1.1 MPa. Earlier studies by Leonard (Annals New York Academy Science 146:203-213, 1968) and Beech (J. Dent. Res. 51:1438-1442, 1972) demonstrated the degradation of cyanoacrylates in vivo and in vitro with bond strengths decreasing 50% in seven days in water.
It is known that microleakage is one of the main etiologic factors in recurrent caries. Further, the ready accretion of plaque onto the contoured surfaces of such materials places the health of contiguous gingival tissues at risk, and reduces the aesthetic values of restorations due to a predisposition to staining.